Umbilical cords will be used for isolation and culture of endothelial cells to be employed in 4 ongoing studies: Cytomegalovirus infection of human endothelial cells induced lymphocyte-mediated cytotoxicity against affected cells; CMV infection of human endothelial cells induces growth factor (PDGF) production by infected cells; human lung exposed to hypoxia expresses vascular endothelial growth factor; and human lung in different stages of development expresses nitric oxide synthase.